NCP26 is a potent, ATP-competitive prolyl-tRNA synthetase (ProRS, PRS) inhibitor, inhibits recombinant human ProRS in the presence of 100 μM proline with KD of 0.35 nM in TR-FRET assays.
NCP26 shows comparable activity under proline-free conditions (KD=271 nM), and is approximately fivefold more potent than T-3767758 (NCP22, Adachi R, et al. Biochem Biophys Res Commun. 2017;488:393-9.).
NCP26 does not bind to the proline pocket in human ProRS, but instead to the ProRS ATP binding site, with the 2-aminoindane moiety occupying an additional adjacent pocket.
NCP26 demonstrates anti-proliferative effect is not altered by proline levels in the tumour environment.
NCP26 significantly decreased cell growth with an EC50 of ~0.5 µM in most MM cell lines, induced the integrated stress response (ISR) via GCN2 and leads to subsequent apoptosis.
NCP26 also showed strong anti-proliferative effects against cells resistant to anthracycline (doxorubicin), PIs (BTZ, CFZ) or immunomodulatory drugs (IMiDs; pomalidomide, lenalidomide).
NCP26 also inhibited cell lines from other hematological malignancies such as leukaemia and lymphoma.
TCF3 is downregulated by NCP26 and involved in MM cell proliferation.
NCP26 (2.5 mg/kg and 10 mg/kg, i.p.,once a day) reduced tumour burden and increases survival time in human MM xenografts in SCID mice., with downregulation of NCP26 targets, including MYC, CCND1 and TCF3, and integrated stress response (ISR) engagement.
NCP26 selectively induced the ISR in patient-derived bone marrow MM cells.